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; Title: BrainFuck 6502 Interpreter for the Apple ][ //e
; File: BF6502A2.VER3B.S
;
: CPU: 6502
; Platform: Apple ][ //e
; By: Michael Pohoreski
; Date: Dec, 2008
; Last updated: Jul, 2015
; Description: 187 Byte Interpreter of BrainFuck
; Version 3b
; - No new functionality
; - Cleaned up source code for readability
; - Switched to Merlin directives
; License: BSD "Sharing is Caring!"
; https://github.com/Michaelangel007/brainfuck6502
;
; Discussion:
; https://groups.google.com/d/msg/comp.emulators.apple2/Om3JKqDZoEA/cwa5U1Hr3TAJ
;
; Definition:
; http://en.wikipedia.org/wiki/Brainfuck
;
; > ++pData;
; < --pData;
; + ++(*pData);
; - --(*pData);
; . putchar(*pData);
; , *pData=getchar();
; [ while (*pData) { // if( *pData == 0 ), pCode = find_same_depth ( ']' );
; ] } // if( *pData != 0 ), pCode = find_same_depth ( '[' );
;
; Reference Tests:
; http://esoteric.sange.fi/brainfuck/bf-source/prog/tests.b
;
; Examples:
; http://esoteric.sange.fi/brainfuck/bf-source/prog/
; http://esolangs.org/wiki/Brainfuck#Implementations
; http://www.muppetlabs.com/~breadbox/bf/standards.html
; http://software.xfx.net/utilities/vbbfck/index.php
; http://nesdev.parodius.com/6502.txt
; ===================================================================
; Source
; This was hand-assembled so don't blame me if this doesn't assemble.
; Well, technically you can, but I'm to lazy to fix it.
; Send me a patch and I'll try to update it.
; Merlin has a 64 char limit of OPERAND+COMMENT
; So you'll probably run into that issue
; One day you'll be able to assemble this directly inside AppleWin
OPCODE EQU $F0 ; Applesoft SPEED @ $F1, Flash mask $F3
OPFUNCPTR EQU $F8 ; Applesoft ROT @ $F9
; Applesoft Free soace $EB .. $EF
CUR_DEPTH EQU $EE ; // current nested depth
NUM_BRACKET EQU $EF ; // depth to find[]
BFPC EQU $3C ; BFPC/pCode same as A1L/H
DATA EQU $40 ; DATA/pData same as A3L/H
HGR EQU $F3D8
HGR2 EQU $F3E2
COUT EQU $FDED
RDKEY EQU $FD0C
NXTA1 EQU $FCBA
NXTA1_8 EQU $FCC2 ; standard entry point is NXTA1 = $FCBA
STOR EQU $FE0B
STOR_6 EQU $FE11 ; standard entry point is STOR = $FE0B
CLRTEXT EQU $C050
SETTEXT EQU $C051
HGR EQU $F3E2
HGR2 EQU $F3D8
RDKEY EQU $FD0C
COUT EQU $FDED ; trashes A, Y
; Used to read start address of $0806 = first Applesoft token
; If you use Applesoft as a helper text entry such as
; 0 "...brainfuck code..."
; You must manually move the BF code to $6000 via:
; CALL -151
; 6000<806.900M
; 300G
ORG $300
; STA CLRTEXT ; 8D 50 C0 ; Optional: C051 or C050
JSR HGR ; 20 D8 F3 ; Clear top 8K of data
JSR HGR2 ; 20 E2 F3 ; Clear bot 8K of data
LDY #$00 ; A0 00 ;
STY BFPC ; 84 3C ;
STY DATA ; 84 40 ;
STY CUR_DEPTH ; 84 EE ;
; Code needs to end with a zero byte
; DEFAULT: $60/$20 for big code ($6000..$BFFF = 24K) / medium data ($2000..$5FFF = 16K)
; Optional: $08/$10 for small code ($0800..$0FFF = 2K) / large data ($1000..$BFFF = 44K)
; Note: You will also need to zero memory if you use large data
LDA #$60 ; A9 60 ; Start CODE buffer
STA BFPC+1 ; 85 3D ;
LDA #$20 ; A9 20 ; Start DATA buffer
STA DATA+1 ; 85 41 ;
FETCH
LDA (BFPC),Y ; B1 3C ;
BEQ EXIT ; F0 1F ;
JSR INTERPRET ; 20 24 03 ;
JSR NXTA1_8 ; 20 C2 FC ;
LDY #$00 ; A0 00 ; because COUT trashes Y
BEQ FETCH ; F0 F2 ; branch always
INTERPRET
LDX #$07 ; A2 07 ; 8 Instructions
FIND_OP
CMP OPCODE,X ; D5 F0 ; table of opcodes (char)
BEQ EXEC ; F0 03 ;
DEX ; CA ;
BPL FIND_OP ; 10 F9 ;
RTS ; 60 ; ignore non-tokens, allows for comments
EXEC
LDA #$03 ; A9 03 ; high byte of this code address
PHA ; 48 ;
LDA OPFUNCPTR,X ; B5 F8 ; function pointer table (address)
PHA ; 48 ;
CLC ; 18 ; optimization: common code
LDA (DATA),Y ; B1 40 ; optimization: common code
EXIT
RTS ; 60 ; 1) exit to caller,
; 2) relative jsr to our bf_*(), or
; 3) exit our bf_*()
BF_NEXT
JMP STOR+6 ; 4C 11 FE ; optimization: INC A3L, BNE +2, INC A3H, RTS
BF_PREV
LDA DATA ; A5 40 ;
BNE .1 ; D0 02 ;
DEC DATA+1 ; C6 41 ;
.1
DEC DATA ; C6 40 ;
EXIT_2
RTS ; 60 ;
BF_INC
ADC #$02 ; 69 02 ; optimization: n+2-1 = n+1
CLC ; 18 ; optimization: fall-through into BF_INCDEC
BF_DEC
SBC #$00 ; E9 00 ;
STORE_DATA
LDY #$00 ; A0 00 ;
STA (DATA),Y ; 91 40 ;
RTS ; 60 ;
BF_IN
JSR RDKEY ; 20 0C FD ; trashes Y
AND #$7F ; 29 7F ; convert 8-bit Apple Text to 7-bit ASCII
BPL STORE_DATA ; 10 F4 ; always
; BrainFuck spec is ambigous -- is Return/Enter stored as 0x0D or 0x0A ?
; CMP #$0D ; C9 0D ;
; BNE STORE_DATA ; D0 F5 ;
; LDA #$0A ; A9 0A ;
; BPL STORE_DATA ; 10 F2 ; optmization: BPL BF_INCDEC (10 F4)
BF_OUT
ORA #$80 ; 09 80 ; output Hi-Bit Apple Text !
; CMP #$8A ; C9 8A ; BrainFuck spec is again ambigous
; BNE .1 ; D0 02 ; what ASCII char is newline? 0x0D 0x0A?
; LDA #8D ; A9 8D ; map newline 0A to 8D
.1
JMP COUT ; 4C ED FD ; trashes A, Y
BF_IF ; ; if( *pData == 0 ) pc = ']'
INC CUR_DEPTH ; E6 EE ; *** depth++
LDA (DATA),Y ; B1 40 ; optimization: common code
BNE EXIT_2 ; D0 E3 ; optimization: BEQ .1, therefore BNE RTS
LDA CUR_DEPTH ; A5 EE ; match_depth = depth
STA NUM_BRACKET ; 85 EF ;
.2 ; Sub-Total Bytes #101
JSR NXTA1+8 ; 20 C2 FC ; optimization: INC A1L, BNE +2, INC A1H, RTS
LDA (BFPC), Y ; B1 3C ;
CMP '[' ; C9 5B ; ***
BNE .4 ; D0 04 ;
INC NUM_BRACKET ; E6 EF ; *** inc stack
BNE .2 ; D0 F3 ;
.4
CMP ']' ; C9 5D ; ***
BNE .2 ; D0 EF ;
LDA CUR_DEPTH ; A5 EE ;
CMP NUM_BRACKET ; C5 EF ;
BEQ EXIT_2 ; F0 C8 ;
DEC NUM_BRACKET ; C6 EF ; *** dec stack
CLC ; 18 ;
BCC .2 ; 90 E4 ;
BF_FI ; ; if( *pData != 0 ) pc = '['
DEC CUR_DEPTH ; C6 EE ; depth--
LDA (DATA),Y ; B1 40 ;
BEQ EXIT_2 ; F0 BD ; optimization: BNE .1, therefore BEQ RTS
LDA CUR_DEPTH ; A5 EE ; match_depth = depth
STA NUM_BRACKET ; 85 EF ;
.2
LDA BFPC ; A5 3C ;
BNE .3 ; D0 02 ;
DEC BFPC+1 ; C6 3D ;
.3
DEC BFPC ; C6 3C ;
LDA (BFPC),Y ; B1 3C ;
CMP ']' ; C9 5D ;
BNE .4 ; D0 04 ;
DEC NUM_BRACKET ; C6 EF ; dec stack
BNE .2 ; D0 EE ;
.4
CMP '[' ; C9 5B ;
BNE .2 ; D0 EA ;
LDA CUR_DEPTH ; A5 EE ;
CMP NUM_BRACKET ; C5 EF ;
BEQ EXIT_2 ; F0 9D ;
INC NUM_BRACKET ; E6 EF ; dec stack
CLC ; 18 ;
BCC .2 ; 90 DF ;
ORG $F0
OPCODE ASC ',.[<]>-+' ; ; sorted: 2B 2C 2D 2E 3C 3E 5B 5D
OPFUNCPTR ; ; by usage: least commonly called to most
DFB BF_IN -1 ; 4D ; ,
DFB BF_OUT -1 ; 54 ; .
DFB BF_IF -1 ; 59 ; [
DFB BF_PREV-1 ; 3A ; <
DFB BF_FI -1 ; 7F ; ]
DFB BF_NEXT-1 ; 37 ; >
DFB BF_DEC -1 ; 46 ; -
DFB BF_INC -1 ; 43 ; +
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